1. Field of the Invention
The present invention relates to a diffusing plate structure, and more particularly, to a diffusing plate structure applied to a backlight module.
2. Description of the Prior Art
Generally, the liquid crystal module utilized in the flat display device adopts the technique of thin film transistor liquid crystal display (TFT-LCD). The lighting mechanism of TFT-LCD is inactive. The brightness that the TFT-LCD needs is provided by a backlight module. Then a colorful image that the TFT-LCD displays is achieved by the filtration of a color filter which filters the light provided by the backlight module.
A conventional direct type backlight module includes a light source and an optical film set. The light source usually adopts light emitting diode (LED). LED becomes one of the most popular light sources that utilizes in the backlight module of TFT-LCD because of smaller size and less energy consuming. When the LEDs are utilized in the backlight module, the LEDs are arranged as a matrix. If light rays respectively emitted from the LEDs in the matrix do not fitly couple with each other, the brightness that the LEDs provide will be uneven. In order to ensure that the backlight module can provide an even brightness distribution, one way is to increase more optical films, and the other way is to add a micro structure disposed on the optical film.
According to a patent of china named “Diffusion plate with dot-matrix diffusion structures and backlight module utilizing same” of which application number is CN201210257025.0, a diffusion plate with dot-matrix diffusion structures have been disclosed. The dot-matrix diffusion structures are disposed on an emergence surface or an incidence surface of the diffusion plate. Centers of the diffusion structures are respectively corresponding to centers of the light sources. The diffusion structure includes two types. The first type is that the diffusion plate includes a circle portion located on a centric area thereof. The circle portion includes hollow spots arranged as a concentric annular. Outside of the centric area of the diffusion plate includes solid spots arranged as a concentric annular. The diffusion structures are applied over the areas with the solid spots and the areas without hollow spots. The second type is that the diffusion plate includes an annular portion disposed on a centric area thereof and arranged as concentric. Outside of the centric area of the diffusion plate includes solid spots arranged as a concentric annular. The diffusion structures are applied over the annular portion and the areas with the solid spots. Although the first and the second types of the diffusion structures mostly overcome the shortage of the uneven brightness distribution phenomenon caused by the conventional LED matrix, light spots emitted from every two adjacent LEDs are still interfered with each other to partially cause that the distribution of the brightness is not symmetry respectively relative to the LEDs.